The use of HALS and UVA individually or in combination to stabilize synthetic resins, plastics, and the lacquers and coatings made therefrom against light degradation is well known. Formerly, UVA such as benzotriazoles, benzophenones, tris-aryl-triazines, and the like were used to stabilize materials susceptible to degradation by light, particularly ultraviolet (UV) light. When the class of compounds known as HALS was discovered, the use of UVA became secondary in use to the HALS. Thus, for example, patents relating to HALS and their use usually disclosed that UVA may be used in addition to the HALS if desired.
U.S. Pat. Nos. 3,118,887 and 3,268,474 disclose the stabilization of plastic and resinous compositions against the effects of ultraviolet light by the incorporation therein of one or more members of a class of tris-aryl-triazines. The aryl radicals of the tris-aryl-triazines UVA are carbocyclic groups of less than three 6-membered rings and at least one of the aryl radicals is substituted by a hydroxyl group which is ortho to the point of attachment to the triazine nucleus. The remaining substituents are either hydroxy, alkyl, alkoxy, sulfonic, carboxy, halo, haloalkyl or acylamino (wherein the acyl is derived from a carboxylic acid). See for example, Formula I in Column 1 and Formula II in Column 2 of U.S. Pat. No. 3,118,887, and Formulas I and II in Column 2 of U.S. Pat. No. 3,268,474.
U.S. Pat. No. 4,355,071 discloses a substrate having a finish of a clear coat top layer in firm adherence to a color coat layer that is in adherence with the substrate. The clear coat consists essentially of a transparent film forming binder. The color coat consists essentially of a film-forming binder, pigment and ultraviolet light stabilizer. The ultraviolet light stabilizer migrates from the color coat to the clear coat. This migration continues as ultraviolet light stabilizer is lost from the clear coat due to exposure to weathering. This provides an adequate level of ultraviolet light stabilizer to retard deterioration of the finish. The resulting finish is particularly useful for automobile and truck finishes. The ultraviolet light stabilizers that are useful include benzophenones, triazoles, triazines, and benzoates among others--see the examples given in Columns 3 and 4.
U.S. Pat. No. 4,314,933 discloses a method for stabilizing two-layer uni-lacquer coatings based on acrylic, alkyd or polyester resins, melamine/formaldehyde resins, epoxide resins or polyisocyanates against the adverse effects of light, humidity and oxygen. The method comprises incorporating into said resin (1) a 2,2,6,6-tetraalkylpiperidine compound, its acid addition salts or metal complexes, and (2) a ultraviolet light absorbing compound. The 2,2,6,6-tetraalkylpiperidine compounds are generally known. See for example Column 1 (Formulas I and II); Column 3 (Formula III); Column 5 (Formula IV); Column 6 (Formulas VA-C); Column 7 (Formula VI); Column 11 (Formula VII); Column 12 (Formula VIII); Column 14 (polymeric compounds in which the recurring structural unit contains a polyalkylpiperidine radical of Formula I); and Column 15 (compounds which contain, in their molecule, at least one 2-(2'-hydroxyphenyl)-benztriazole group or 2-hydroxybenzophenone group and at least one polyalkylpiperidine group). The patent discloses that in order to achieve maximum stability to light, it can be advantageous to use other conventional light stabilizers. Examples of these are UV-absorbers of the type comprising the benzophenones, oxanilides, benztriazoles or acrylic acid derivatives, or metal-containing light stabilizers, for example, organic nickel compounds.
U.S. Pat. No. 4,356,307 discloses stabilizers for synthetic resins, especially for polyolefins. The stabilizers have a cyclic imide bound to the 4-position of a 2,2,6,6-tetramethylpiperidine--see for example the Formula in Column 1.
U.S. Pat. No. 4,419,472 discloses ester mixtures of polyalkylpiperidine derivatives in which the ester substituent is in the 4-position of the polyalkylpiperidine--see Formulas I and II in Column 1. These mixtures are suitable as stabilizers for plastics. Other stabilizers which are known can also be incorporated in the plastics with the ester mixtures. These include UV-absorbers and light stabilizers, such as, 2-(2'-hydroxyphenyl)benztriazoles, 2-hydroxybenzophenones, and sterically hindered amines, among others--see Columns 6-7. The patent discloses that known and conventional additives of this type are not only compatable with the mixtures of esters but, in individual cases, can also result in a synergistic effect.
U.S. Pat. No. 4,426,471 discloses a stabilized lacquer composition comprising: (a) an acid catalyzed stoving lacquer based on hot crosslinkable acrylic, polyester or alkyd resins; (b) an N-substituted 2,2,6,6-tetraalkylpiperidine compound or its acid addition salt; (c) a UV absorber selected from the group consisting of the benzophenones, benzotriazoles, acrylic and derivatives, organic nickel compounds and oxanilides; and (d) a phenolic antioxidant. The N-substituted 2,2,6,6-tetraalkylpiperidine compounds are generally known. See for example Column 1 (Formula I); Column 2 (Formula II); Column 3 (Formula VIII); Column 5 (Formula IV); Column 6 (Formula V); Column 7 (Formula VI); Column 9 (Formula VII); Column II (Formula VIII); Column 12 (polymeric compounds, the recurring structural units of which contain a group of the Formula I or which are linked through a bivalent group corresponding to Formula I); and Column 15 (compounds which contain in their molecule at least one 2-(2'-hydroxyphenyl)-benztriazole group or 2-hydroxybenzophenone group and at least one polyalkylpiperidine group). Examples of UV absorbers which may be used in conjunction with the aforementioned piperidine compounds are provided in Columns 17-18.
U.S. Pat. No. 4,426,472 discloses a method for stabilizing metallic stoving lacquers based on hot-cross-linkable alkyd resins or acrylic resins against the action of light, moisture and oxygen. The method comprises incorporating in the resin an effective stabilizing amount of a 2,2,6,6-tetraalkylpiperidine compound, or of the acid addition salts or complexes with metal compounds thereof. The patent discloses that to obtain maximum stability to light, the concomitant use of other customary stabilizers can be advantageous. Examples of these are UV absorbers of the benzophenone, oxanilide or benzotriazole type, or acrylic acid derivatives, or metalcontaining light stabilizers, such as organic nickel compounds. The 2,2,6,6-tetraalkylpiperidine compounds are generally known. See for example Column 1 (Formulas I and II); Column 3 (Formula III); Column 5 (Formulas IV and V): Column 7 (Formula VI); Column 11 (Formula VII); Column 13 (Formula VIII); and Column 14 (polymeric compounds of which the recurring structural unit contains a polyalkylpiperidine radical of Formula I).
European Patent Application No. 82304941.6, Publication No. 0078603, Published May 5, 1983, Bulletin 83/19, discloses a composition comprising a substantially crystalline polymer of an aliphatic monoalpha-olefin and a hindered amine or its salt, N-oxide, N-hydroxide, or N-nitroxide. The hindered amine has its amino nitrogen contained in a carbon-nitrogen carbon chain which forms part of a non-aromatic heterocyclic ring. Also, each of the two carbon atoms of the chain is bonded to two lower alkyl groups, which may be the same or different, each lower alkyl group containing from 1 to 12 carbon atoms, or to an alicyclic group containing from 4 to 9 carbon atoms which groups sterically hinder the amine. The composition may also contain, for example, stabilizing amounts of light stabilizers, e.g., benztriazoles.
European Patent Application No. 83300861.8, Publication No. 0087294, Published Aug. 31, 1983, Bulletin 83-85, discloses an irradiation sterilizable composition comprising a semi-crystalline polymer. Incorporated in the polymer is a mobilizing amount of a non-crystalline liquid mobilizing additive which increases the free volume of the polymer. Also, incorporated in the polymer is a sterically hindered amine or its N-oxide, N-hydroxide or N-nitroxide salt. The amine nitrogen of the hindered amine is contained in a carbon-nitrogen-carbon chain which forms part of a non-aromatic heterocylic ring. Each of the two carbon atoms of the chain is bonded either to two alkyl groups which are the same or different and each having 1 to 12 carbon atoms, or to an alicyclic group containing 4 to 9 carbon atoms. The composition may contain stabilizing amounts of, for example, light stabilizers, e.g., benzotriazoles.
Berner, G., and Rembold, M. "New Light Stabilizers For High-Solid Coatings", in Organic Coatings, Science and Technology, Volume 6, (1984), Edited by Parfitt, G. D. et al, pp.p. 55-85, TP 1175. S607, discloses the synergistic combination of a sterically hindered amine light stabilizer (radical scavenger) with a benztriazole UV-absorber. It is also disclosed that a new HALS-type combined with a benztriazole (designated Benztriazole I--see page 58) in a 1-package high-rated paint proved to be an outstanding stabilizer package. The high-solid paint was based upon a hydroxyl-functional acrylic resin and a HMMM resin (a fully alkylated melamine resin) as the crosslinker. Further disclosed, at pages 83-84, is that light stabilizers are complementary to each other. This synergism can possibly be explained based upon the assumption that fewer radical processes are photochemically induced in the presence of UVA. It has been shown by model experiments that the (relative) stabilizing effect of HALS may depend on the number of radical processes induced with time. Therefore, at high rates of radical initiation (in the absence of UV absorber) the observed efficiency of HALS is lower since the higher radical concentrations are not as effectively controlled by the stabilizers.
Although the use of HALS and UVA in combination with each other is well known, there has been relatively little known work on or discovery of combinations of particular HALS and UVA that will produce synergistic results. An exception to this, as noted above, is the use of a benztriazole with a HALS of unknown structure in a high-solid paint (Berner et al above). A welcome contribution to the art would be synergistic combinations of HALS and UVA to provide polymers with protection against degradation by light. Such a contribution is provided by this invention.